If you want a front line high AC tank then you don't want a trickery cleric. That simply isn't the role that subclass is designed for. You're wanting to do far more than just change stats at that point.
Seems to me that you are mixing "asigned job" and "optimal role" ... but quite honestly:
I dont care ...
I got Cleric and i want him to do this job ... thats all i need to know.
Is it ineffective? Maybe ...
Will i find out? Maybe ...
Will i change her job afterwards? Also maybe ...
But until then ... if i WANT to send her in front lines with as much AC as possible, i shall. And there is no rule in the world that can stop me. :P